Isoprene (2-methyl-1,3-butadiene) is an important organic compound used in a wide array of applications. For instance, isoprene is employed as an intermediate or a starting material in the synthesis of numerous chemical compositions and polymers. Isoprene is also an important biological material that is synthesized naturally by many plants and animals.
Isoprene became an important monomer for utilization in the synthesis of cis-1,4-polybutadiene when its stereo-regulated polymerization became commercially possible in the early 1960s. cis-1,4-Polyisoprene made by such stereo-regulated polymerizations is similar in structure and properties to natural rubber. Even though it is not identical to natural rubber it can be used as a substitute for natural rubber in many applications. For instance, synthetic cis-1,4-polyisoprene rubber is widely used in manufacturing vehicle tires and other rubber products. This demand for synthetic cis-1,4-polyisoprene rubber consumes a majority of the isoprene available in the worldwide market. The remaining isoprene is used in making other synthetic rubbers, block copolymers, and other chemical products. For instance, isoprene is used in making butadiene-isoprene rubbers, styrene-isoprene copolymer rubbers, styrene-isoprene-butadiene rubbers, styrene-isoprene-styrene block copolymers, and styrene-isoprene block copolymers.
The isoprene used in industrial applications is typically produced as a by-product of the thermal cracking of petroleum or naphtha or is otherwise extracted from petrochemical streams. This is a relatively expensive, energy-intensive process. With the worldwide demand for petrochemical based products constantly increasing, the cost of isoprene is expected to rise to much higher levels in the long-term and its availability is limited in any case. There is concern that future supplies of isoprene from petrochemical-based sources will be inadequate to meet projected needs and that prices will rise to unprecedented levels. Accordingly, there is a need to procure a source of isoprene from a low cost, renewable source which is environmentally friendly. The improved methods and compositions described herein provide such a source of isoprene, capable of being derived at low cost and from renewable sources.
Several recent advancements have been made in the production of isoprene from renewable sources (see, for example, International Patent Application Publication No. WO 2009/076676 A2). Such methods produce isoprene at rates, titers, and purity that may be sufficient to meet the demands of a robust commercial process, however process improvements to reduce the operational costs associated with the production of isoprene derived from biological sources and to increase yields of isoprene are needed, such as the improved compositions and methods for the increased production of isoprene and other heterologous polypeptides capable of biological activity provided herein.
All patents, patent applications, documents, nucleotide and protein sequence database accession numbers and articles cited herein are incorporated herein by reference in their entirety.